I used a Happy Troller on my old 17' foot boat with an 80Hp Merc for a couple years before I got an Alumaweld with a kicker. The Happy Troller worked well on the 80HP. It got me slow enough for trout and sockeyes on the lakes and salmon in the salt.

They do come in sizes so get one that fits your engine and prop size. If you're going to be doing much trolling with a big motor, especially if it's a 2 stroke, be sure to change your plugs more often. All that slow use on the motor will foul them much more quickly.

All in all, I was happy using the trolling plate over the prop and it did what I need to do.